Fuse in lead-in of incandescent lamp filament



' May 3,1966 "3,249,798

FUSE 1N LEAD-IN OF INCANDESGENT LAMP FILAMENT G. H- BURNEYTT Filed Sept}19. 1962 lnven lrov Geov" e H. Bw'ne t t 8 His t'c ar'neg United StatesPatent Filed Sept. 19, 1962, Ser. No. 224,137 3 Claims. ((31. 3151-73)This invention relates in general to electric incandescent lamps andsimilar devices, and more particularly to an electric incandescent lampof the self-contained reflector type having an internalfuse.

Incandescent lamps, especially the high wattage types, require a fusesince at the end of life an arc may form --between the burnt ends of thefilament and result in violent failure. As the arc starts to form, morecurrent is drawn through the lamp, whereby-the fuse burns out andviolent failure is prevented. Since it is inconvenient for the user toreplace an external fuse as well as the-lamp after the lamp burns out,it is desirable to incorporate the fuse into the lamp itself. Theincorporation of a fusible material into the lead-in wires of anincandescent internal reflector lamp could result in a substantialweakening of the support for the filament.

Therefore, it is an object of this invention to provide a fuse withinthe lamp itself which does not substantially weaken the filamentsupport. It is a further object to provide a structure which may easilyand economically be assembled. i

' Briefly stated, in accordance with the invention at least one of thelead-in wires of the lamp is provided with a fusible material sectionwhich is surrounded by a closely fitting hollow sleeve or standard ofinsulating material fused in the thimble supporting the leadin wire,

thereby adequately supporting thefilament.

Further objects and advantages of the invention will appear from thefollowing detailed description of the preferred embodiment of theinvention and from the accompanying drawing wherein:

FIG. 1 is a perspective view, certain parts broken away, of .an electricincandescentlamp having an internal fuse comprising the invention;

FIG. 2 is a sectional view of the lamp; and

FIG. 3 is a fragmentary sectional view on an enlarged scale of the leadwire provided with the fusible material section.

Referring to the drawing, the invention is there illustrated asembodiedin an electric incandescent lamp of the self-contained reflector typesuch as described and claimed in US. Patent 2,148,314, Wright, issuedFeb. 21, 1939, and assigned to the assignee of the present invention.The lamp comprises a bulb or envelope 1 consisting of a preformedpressed glass reflector section 2 sealed around its periphery to apreformed pressed glass cover section 3. The interior surface of thereflector section 2 is of suitable light-concentrating shape such asparaboloidal,

for instance, and it is covered with a metallic coating 4 of aluminum orsilver to constitute a reflecting surface. Mounted on the reflectorsection 2, exteriorly thereof and at the apex of said section, is a basestructure 5. The base structure 5 may be of the type described andclaimed in US. Patent 2,272,512, Cotman et al., dated February 1-0,1942, and comprising a pair of metallic lugs (not shown) suitablysecured as by soldering to metallic cups or thimbles 7 having theiredges sunk and embedded in the glass of the reflector section 2 aroundopenings 8 therein, the cups or thimbles thus hermetically closing saidopenings 8. The envelope 1 is exhausted and filled with a suitable inertgas through an exhaust tube 9 attached to the reflector section 2 at itsapex. After the gas filling is introduced into the lamp envelope,

the exhaust tube 9 is tipped off, as indicated at 10, to hermeticallyseal the envelope.

Mounted within the envelope 1 and supported therein from the metalthimbles 7 is a mount structure comprising an electric energytranslation element or filament 11 disposed between and connected to apair of rigid leadin wires or conductors 12 and 13 of suitable material,such as nickel or iron. The lead-in conductors 12 and ,13 are rigidlysecured at their outer ends to the metal thimbles 7, as by soldering orby brazing, and they may extend straight through the opening 8 in thereflector section into the interior of, and in more or less parallelrelation to one another and preferably in a plane parallel to andincluding the axis of the reflector section 2. The lead-in conductors 12and 13 are held in rigid spaced relationby an insulating bridge orcrossbar member comprising a glass rod 14 extending be tween and secured tothe lead-in conductors by short fastening wires 15 which may bespot-welded to the lead-in conductors. Inwardly of the envelope 1, thelead-in conductors 13 are offset away from each other to form offsetouter end portions 16 to which the ends of the filament 12 areconnected.

The filament 12 is constituted of tungsten wire, and

in-the particular case illustrated comprises a linear coiledembedded inthe glass rod 14 is attached to one of the center turns of thecoiled-coil filament to secure and maintain the intermediate portion ofthe filament in correctposition with respect to the focus of thereflector surface 4. A screen 18 supported from lead-in conductor 12by-the member 194's provided to prevent the tungsten vapors given off bythe filament in operation from condensing on the envelope 1 and causingbulb blackening. It will be understood that the lamp as shown isdesigned for operation with the axis of the reflector and the axis ofthe filament ina horizontal position and with the screen 18 positionedabove the filament 12.

With a lamp of this type having a high wattage filament, it is necessaryto fuse the lamp so that violent failures at the end of lamp life do notoccur. This has been customarily done by some external fusing means. Thelamp, asflsho'wn, in accordance with this invention, has an internalfuse 20 (FIG. 3) butt-Welded between portions 13a and 13b of lead wire13. The fuse 20 may be any suitable fusible material of properdimensions so as to fail when the peak inrush of current at end of lamplife occurs. Surrounding the composite structure of lead wire part 13a,fuse 20 and lead wire 13b is a hollow standard or sleeve 21 ofinsulating material which may be, for example, a glass tube'having aninside diameter slightly larger than the outside diameter of the leadwire sections 13a and 13b. The outer end of standard 21 is fused orembedded in the solder joint 22 of the thimble 7 for the lead wire 13.

It has been found that it is unnecessary to secure standard 21 at itsinner end to lead wire section 13b and therefore it will be noted inFIG. 3 that the. inner end of standard 21 surrounds and is spacedslightly from 'oonductor 13b. The spacing between the inner end ofstandard 21 and conductor 13b may be defined as a slip-fit spacing, thatis, a spacing such that in assembly the standard 21 may be easilyinserted over the composite structure of lead wire 13a, fuse 20 and leadwire 13b. This construction provides lead-in wire 13 with adequate 3strength to support the filament 11 because the fuse section 20 hasadequate strength in longitudinal compression and tension, the mainweakness of the composite structure being against bending stresses.Since the mount structure is supported on one side by a rigid conductorwire 12 fused to the other thimble 7 bending stresses applied by theweight of the filament and screen or by external forces, place thesestresses on conductor 13b which displaces it within standard 21. Theinner end of standard 21 is sufiiciently close to lead wire portion 13bso that any canting of conductor 13 is prevented by the inner end ofstandard 21, and the filament and screen is maintained in its properposition. Thus, it will be noted that there is provided a lamp of thereflector type having a high wattage filament which is provided with aninternal fuse which does not weaken the support necessary for thefilament and other auxiliary equipment within the lamp.

The above construction has the additional advantage of being easily andeconomically manufactured on standard reflector lamp equipment since theonly additional operation to be performed on the actual assembly machineis the insertion of the standard 21 around lead wire 13, the mountstructure for the lamp being provided with the fusible section 20 in oneof the conductor wires prior to assembly into the envelope. The mountstructure having the fusible section therein and the standard 21surrounding the lead wire may then be aligned in the reflector section 2of the lamp with the conductor wires 12 and 13 within respectivethimbles 7. Then, as is customary, the solder pellet may be placed inthe thimble 7 and heat applied thereto. The solder pellet may be, forexample, of the type disclosed in U.S. Patent 2,745,742, issued May 15,1956, which comprises a sintered powder mass of brass solder and borateglass flux. The melting of the solder .pellet secures the conductorlead-in wires, as is conventional, and additionally in the same singleoperation, secures the standard 21 to the thimble as well. Thus, the newand advantageous structure may be assembled with a minimum of difficultyand cost.

While the invention has been disclosed by way of its preferredembodiment, it will be understood that it maybe widely modified with-inthe spirit and scope of the appended claims.

What is desired to be secured by Letters Patent of the United States is:

1. An electric incandescent lamp comprising a sealed envelope having abase structure including a pair of thimbles hermetically closingadjacent openings in a wall of said envelope, a pair of lead wireshaving outer end portions anchored in respective said thimbles andextending into the interior of said envelope, a filament supported bysaid lead wires, at least one of said lead wires having a fusiblesection adjacent its outer end and adjacent the associated thimble, anda hollow standard of insulating material closely surrounding the outerend portion of said one lead wire including said fusible section andhaving one end thereof extending from and anchored in the associatedthimble.

2. An electric incandescent lamp comprising a sealed envelope having abase structure including a pair of thimbles hermetically closingadjacent openings in a wall of said envelope, a pair of lead wireshaving outer end portions anchored in respective said thimbles andextending into the interior of said envelope, at filament supported bysaid lead wires, at least one of said lead wires having a fusiblesection butt-welded between spaced portions of its outer end adjacentthe associated thimble, a glass tube closely surrounding the spacedportions of said one lead wire and the interposed said fusible sectionand extending from within said associated thimble, and means securingthe ends of said one lead wire and the glass tube to the said associatedthimble.

3. An electric incandescent lamp comprising a sealed envelope having abase structure including a pair of thimbles hermetically closingadjacent openings in a wall of said envelope, a pair of lead wireshaving outer end portions anchored in respective said thimbles andextending into the interior of said envelope, a filament supported bysaid lead wires, at least one of said lead wires having a fusiblesection butt-welded between spaced portions of its outer end adjacentthe associated thimble, a glass tube closely surrounding the spacedportions of said one lead wire and the interposed said fusible sectionand extending from within said associated thimble, and a quantity offused solder securing the ends of said one lead wire and the glass tubeto the said associated thimble.

References Cited by the Examiner UNITED STATES PATENTS 2,183,952 12/1939Anderson 315 73 2,870,362 1/1959 Arnold 313 113 DAVID J. GALVIN, PrimaryExaminer.

1. AN ELECTRIC INCANDESCENT LAMP COMPRISING A SEALED ENVELOPE HAVING ABASE STRUCTURE INCLUDING A PAIR OF THIMBLES HERMETICALLY CLOSINGADJACENT OPENINGS IN A WALL OF SAID ENVELOPE, A PAIR OF LEAD WIRESHAVING OUTER END PORTIONS ANCHORED IN RESPECTIVE SAID THIMBLES ANDEXTENDING INTO THE INTERIOR OF SAID ENVELOPE, A FILAMENT SUPPORTED BYSAID LEAD WIRES, AT LEAST ONE OF SAID LEAD WIRES HAVING A FUSIBLESECTION ADJACENT ITS OUTER END AND ADJACENT THE ASSOCIATED THIMBLE, ANDA HOLLOW STANDARD OF INSULATING MATERIAL CLOSELY SURROUNDING THE OUTEREND PORTION OF SAID ONE LEAD WIRE INCLUDING SAID FUSIBLE SECTION ANDHAVING ONE END THEREOF EXTENDING FROM AND ANCHORED IN THE ASSOCIATEDTHIMBLE.